Doing some cloud research and I came across the High Scalability website which collects information on some of the largest Internet companies out there. Very interesting. Today, I saw a post that points to the Data Center Knowledge site listing numbers of Web servers for Internet companies, especially those in the "50,000 server club". Some highlights:

Google: 450,000 or 600,000?

UK government SIGINT/Comms organisation at GCHQ: 245,000 (wonder if this guy will get caught/fired for divulging this information and its location)

Microsoft: 218,000

They have many others. Don't forget to read the comments that have a number of other numbers.